<template>
    <ul class="list">
        <li class="item" 
        v-for="item of letters" 
        :key="item"
        :ref="item" 
        @click="handleletterClick"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        >{{item}}</li>
    </ul>
</template>

<script>
export default {
    name:"CityAlphabet",
    props:{
        cities:Object
    },
    data(){
        return{
            touchStatus:false,
            startY:0
        }
    },
    computed:{
        letters(){
            const letters = []
            for (let i in this.cities) {
                letters.push(i)
            }
            return letters
            }
    },
    methods:{
        handleletterClick(e){
            this.$emit("change",e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus = true
        },
        handleTouchMove(e){
            if (this.touchStatus){
                const startY = this.$refs['A'][0].offsetTop
                console.log(startY)
                const touchY = e.touches[0].clientY - 79
                const index = Math.floor((touchY - this.startY) / 20)
                if (index >= 0 && index < this.letters.length) {
                    this.$emit('change', this.letters[index])
                }
            }
        },
        handleTouchEnd(){
            this.touchStatus = false
        }
    }
}
</script>

<style scoped>
    .list{
        display:flex;
        flex-direction:column;
        justify-content:center;
        position:absolute;
        top:1.58rem;
        right:0;
        bottom:0;
        width:.4rem;
    }
    .list .item{
        text-align:center;
        line-height:.4rem;
        color:#00bcd4;
    }
</style>